The present invention relates to one-component RTV silicone rubber compositions and more particularly, the present invention relates to alkoxy-functional one-component RTV silicone rubber compositions in which the base polymer composition comprises a blend of polyalkoxy functional polymers and mono-alkoxy functional polymers.
There are a large number of one-component RTV (RTV shall be used hereinafter to refer to room temperature vulcanizable) silicone rubber compositions. One type of such one-component RTV silicone rubber composition comprises an alkoxy-functional system in which the cross-linking agent is polyalkoxy silane. An example of such one-component alkoxy-functional RTV composition is that disclosed in BEERS, U.S. Pat. No. 4,100,129 and Brown, U.S. Pat. No. RE 29,760. The BEERS patent discloses the basic system of a silanol end-stopped polymer, a polyalkoxy silane cross-linking agent such as methyltrimethoxysilane and preferably a titanium chelate catalyst. Such a composition has the advantages of being non-corrosive and not emitting pungent odors upon curing as is the case with some of the other types of RTV silicone rubber compositions. However, such a composiiton has the disadvantage that even with the titanium catalyst, it is not as fast curing as would be desirable. In addition, it has a shelf stability problem; that is, even though it will cure after storage, in some cases various agents had to be added to it for that purpose. Further, it was found that even if such compositions did cure, nevertheless, the cure rate was slowed considerably. In some cases after prolonged storage, it was found that compositions did not cure at all. The reason for the retardation in the cure rate of such compositions was the fact that the free hydroxyl groups in the RTV system results in the degradation of the alkoxy radicals at the terminal ends of the diorganopolysiloxane base polymer in the composition. As a result, the composition will not cure or cross-link properly or at a sufficient rate to give a final cured composition with desirable physical properties.
Accordingly, inventions were made or effected to make such compositions more shelf-stable which included the addition of various ingredients or various types of procedures in the preparation of such compositions. An example of the production or the making of such compositions such that they are shelf-stable, is to be found in the patent of White, et al, U.S. Pat. No. 4,395,526, which discloses the use of scavengers; and which scavengers will react with and tie up unbonded hydroxy groups in the substantially anhydrously packaged composition. As a result of the scavenger tying up or bonding with such hydroxy groups in a composition, the hydroxy groups will not attack the alkoxy radicals on the terminal silicon atoms of the polyalkoxy base polymer and the composition will be shelf-stable and as a result, fast curing even after prolonged periods of storage.
U.S. Pat. No. 4,395,526 also discloses the utilization of various integrated cross-linkers, scavengers which will function as cross-linking agents for reacting with the silanol groups in the base polymer terminating the polyalkoxy-formed polysiloxane polymer with such scavenging and alkoxy groups such that the polymer will be able to cross-link and cure upon being exposed to atmospheric moisture. In addition, such integrated cross-linkers, scavengers acted as scavengers for scavenging or reacting with the free hydroxyl groups in the system so that they will not be able to degrade the alkoxy groups in the base polymer system.
Another application in this area is that of CHUNG, U.S. Pat. No. 4,424,157, which discloses the use of certain cyclic amides for that purpose. Other applications are that of LUCAS, U.S. Pat. No. 4,483,973, which discloses certain adhesion promoters for the systems of the WHITE, et al, patent and that of DZIARK, U.S. Pat. No. 4,417,042, which discloses the utilization of certain silazane scavengers as pure scavengers for the polyalkoxy terminated polymers of the WHITE, et al, U.S. Pat. No. 4,395,526. In addition, there is the Patent of BEERS, U.S. Pat. No. 4,513,115 which discloses the utilization of certain additives to the system of WHITE, et al, and DZIARK which will make these compositions low-modulus as well as fast-curing and shelf-stable.
Then there is the integrated cross-linker, scavenger or pure scavenger alkoxy functional silazanes of BEERS, et al, U.S. Pat. No. 4,720,531, as well as the end-coupling catalyst for producing the base polymer in all such systems as disclosed in CHUNG, U.S. Pat. No. 4,515,932. There is further disclosed the production of such polymers continuously by preparing them in a static mixer and then a devolatilizing extruder as set forth in CHUNG, et al, U.S. Pat. No. 4,528,324. Finally, there is the Patent of LUCAS, U.S. Pat. No. 4,599,394, entitled "Process for Producing Alkoxy-Terminated Polysiloxanes."
All of these patent applications relate to various aspects of such systems and such one-component alkoxy-functional RTV systems in which there is utilized a scavenger or integrated scavenger, cross-linker to tie up free hydroxy groups in the RTV system such that they will not degrade the alkoxy groups in the base polymer or base polymers and such that the shelf-stability of the composition will not suffer and such that the composition will be fast-curing. In some of these patent applications it is disclosed that there can be tolerated a certain amount of mono-alkoxy terminated polymer in the base polymer composition. While this is true, these patent applications do not disclose how much of the monoalkoxy polymer can be tolerated and in what systems it can be tolerated. The present application relates to and discloses the discovery of how much of such diorganopolysiloxane polymers which are terminated solely with mono-alkoxy groups can be tolerated in the polymer mixture in one-component RTV systems. Further, there is disclosed other systems in which such mono-alkoxy termination can be utilized within the scope of the instant invention. There is the disclosure of NITZSCHE, et al, U.S. Pat. No. 3,127,363. However, this disclosure relates to just mono-alkoxy-terminated polymers which it is stated will not cure without a cross-linking agent.
Accordingly, it is one object of the present invention to provide a fast-curing, shelf-stable, one-component alkoxy functional RTV system in which there is present, in the base polymer blend, a certain amount a mono-alkoxy terminated diorganopolysiloxane polymer species.
It is another object of the present invention to provide for an alkoxy-functional one-component RTV system in which there is present in the base polymer species, a mono-alkoxy terminated diorganopolysiloxane polymer in which the terminal silicon atoms have a scavenging leaving group.
It is still a further object of the present invention to disclose a process for producing an alkoxy-functional one-component RTV system which is fast curing and shelf-stable and in which the base polymer species has a certain amount of mono-alkoxy terminated diorganopolysiloxane polymer species.
It is yet a further object of the present invention to disclose a process for producing an alkoxy-functional one-component RTV system in which the base polymer species and compositions comprises a mono-alkoxy terminated diorganopolysiloxane polymer having terminal silicon atoms which in addition to just the one alkoxy group, have at least one hydrolyzable scavenging leaving group.
These and other objects of the present invention are accomplished by means of the disclosures set forth herein below: